Correct option – B. Iron nail in P (CuSO₄) undergoes displacement: copper ions reduced to copper metal, giving a brownish coating; in Q (AgNO₃) iron displaces silver, producing a silver coating on the nail during the reaction. cbse sample paper 2025 ...
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Correct option – D. Sodium hydroxide. Among the options, NaOH is a strong, highly soluble base producing a high concentration of OH⁻ in solution; magnesium hydroxide is sparingly soluble and both acids give low pH values generally. cbse sample paper 2025 ...
Correct option – B. When excess CO₂ passes through limewater, the initially formed insoluble calcium carbonate (which causes milkiness) reacts further with CO₂ and water to form soluble calcium bicarbonate, clearing the milkiness from the solution completely. cbse sample paper 2025 ...
Correct option – D. Sodium chloride. When aqueous barium chloride reacts with aqueous sodium sulphate, barium sulphate precipitates and sodium chloride remains in the solution. Thus the aqueous solution formed contains NaCl with BaSO₄ as solid precipitate. cbse sample paper 2025 ...
Correct option – D. Assertion A is false — C4H10 is saturated (alkane) while C4H8 (alkene) and C4H6 (alkyne/diene) are unsaturated. Reason R is true because the listed compounds (except C4H10) are unsaturated, so choose option D. cbse sample paper 2025-26 ...